Upvotes are a cheap. You can breeze through the site upvoting all sorts of things.

Really useful questions get favorited. Why not have the reputation system reflect this?

There's a disincentive for people to favorite things that aren't that useful because it degrades the utility of the favoriting system for them so you could probably award more rep than for a standard upvote.

If someone likes the question they'll upvote it more often than not so a favourite is just a second upvote. IMHO there's no need for that. There was an article floating around last month about how complex voting systems are a waste. I think the example was Youtube where the vast majority of votes were 0 or 5 with very little in between.

So basically you could give people two choices—like or dislike—and you'd achieve basically the same end result.

One can also use the favourite button to flag a post as a reminder to return later to check whether it has been improved yet. For example to undo a downvote, or to give the OP some time to improve his question before voting to close.

Obviously, in those cases the OP should not be rewarded additional reputation points. My point is: Marking a post as "favourite" is not always a compliment.

I think another issue with this is how you can set or remove favorites at any time -- this is a necessity in a favorite system, where you might want to bookmark something just to read it again one time.

Contrast this with the upvote system, where once a vote has been set (for a couple minutes), you can't change your vote. I assume part of the reasoning for this is that it would be unfair to the upvotee if you decided you wanted to un-upvote any of their answers at a later date. It would be at least annoying if your rep went up and down frequently due to people starring and unstarring your questions.

Also, there are the Favorite Question and Stellar Question badges that are awarded for 25 and 100 favorites, respectively; so it's not like you never get anything for favorites on your questions.

The lock on changing of votes has only been introduced as some people abused the voting, not because it would be unfair if votes were changed per se. I wouldn't mind if people removed an upvote at some later time, or would even change an upvote to a downvote. But well, to avoid abuse things are like they are, which is fine to me as well: meta.stackexchange.com/questions/6460/…
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ArjanNov 1 '09 at 16:23

Another use of the favorite is to strategically enhance a question. Those with the little colored stars do get a tiny bit more attention than those that aren't favorited by anyone.

I've done some unscientific testing, and over a random set of questions that normally don't get favorited, those which I favorite while still on the front page usually get a slightly higer vote (and more "me-too" favorites) than the control group.

It's not much, but you have to take into account that once you attach rep to something, people will use it to game the system, and it may well damage the usefulness that it originally had.

Right now the favorite stands as a unique indicator, "I thought this question was interesting/useful/pertinent enough that I want to refer to it again later."

I also request that favorites gain reputation points, as often times people only favorite but do not also upvote for the reason outlined before. That is, in my experience, people gravitate toward simplicity and tend to do one thing (i.e., upvote OR favorite) versus two things (i.e., upvote AND favorite).